The two things to learn Ido for English speakers are Ido Skolo and the Dyer dictionaries (and a way to communicate with others, but that's not really a reference is it?)
Look in the reference section for the Ido Skolo 1.8 PDF file. I'm hosting it for everyone. It starts easy and goes through mastery.
To get the Dyer dictionaries from me takes a bit more work; yes this folder has both e-i and i-e!